A packaging process in a process of manufacturing a semiconductor device is a process of improving reliability of a semiconductor device by protecting a semi-conductor chip from the external environment, shaping the semiconductor chip so as to be easily used, and protecting an operation function of the semiconductor chip.
In general, packaging of a semiconductor device is performed using a low temperature co-fired ceramic (LTCC) or a printed circuit board (PCB).
Because a resin substrate used for the semiconductor package has very low thermal conduction characteristics and is deformed at a high temperature, the resin substrate is not generally used when packaging a high power semiconductor device. When using the resin substrate in order to package a high power semiconductor, special processing for enhancing thermal conduction characteristics is necessary and thus the price of the resin substrate is very high.
Further, a ceramic substrate has much better heat resistance than that of the resin substrate, but the ceramic substrate is expensive, and it is difficult and expensive to process.
In order to overcome the drawbacks of the ceramic substrate and the resin substrate, use of a metal material substrate has been suggested. The metal material substrate has merits of being inexpensive, ease of processing, and excellent heat releasing characteristics in which thermal conduction characteristics of the metal material substrate are much better than those of resin or ceramic, and thus has good thermal reliability.
In Korean Patent Nos. 10-0656295, 10-0656300, and 10-0625196, package module technology using a metal substrate is disclosed. The package module technology using a metal substrate is technology regarding completing a module including a semi-conductor chip by forming an oxide film in the metal substrate and providing a package module having high frequency characteristics, semiconductor process compatibility, thermal reliability, and electromagnetic interference (EMI) and electromagnetic compatibility (EMC) stability.
Currently, various application structures and technologies for packaging a metal substrate using an oxide film are being developed, and research thereof is ongoing.
In general, when mounting a high power semiconductor device using a metal having high thermal conduction characteristics, heat generated in the semiconductor device is immediately released through the metal substrate and thus a very effective structure having high reliability and performing stable operation is provided. Particularly, the semiconductor device (for example, a semiconductor chip such as a light emitting diode (LED)) uses Joule heat of a current flowing through an area of a very small size and thus has a very high current density per unit area, whereby to effectively remove some heat is very important to enhance reliability of a final product (when operating at a high temperature, characteristics of the semiconductor device change and the life-span thereof is reduced, and thus a smooth heat-radiating design is a core factor for sustaining performance of a final product).
However, when packaging a high power semiconductor device using the metal substrate, a structure that very effectively releases heat is obtained, compared with a ceramic substrate or a resin substrate, but high stress occurs at an interface between two materials due to a thermal expansion coefficient difference between the metal substrate and the semiconductor device, and this has a harmful influence on reliability (for example, solder joint reliability (SJR)).
That is, the metal substrate has a thermal expansion coefficient of about 2-5 times that of the semiconductor device, and as a general semiconductor device smoothly releases heat, the temperature of the interface does not significantly increase and thus stress does not occur, but in a high power semiconductor device, even if heat is smoothly released, a large amount of heat occurs in the element and thus stress due to the difference in thermal expansion occurs at an interface between the two materials.
For example, the thermal expansion coefficients of Si, GaAs, GaN, which are materials of the semiconductor device, are in a range of about 4-7 ppm/K, while aluminum (Al) and magnesium (Mg), which are materials of the metal substrate, have thermal expansion coefficients of 23 ppm/K and 25 ppm/K, respectively, and thus materials of the semiconductor device and materials of the metal substrate have a very large thermal expansion coefficient difference.
Therefore, if the semiconductor device and the metal substrate are repeatedly in a high temperature state and a low temperature state, the semiconductor device and the metal substrate repeatedly expand and contract by different amounts in proportion to their different thermal expansion coefficients, and because materials enclosing a package in a packaging module expand and contract more than the semiconductor device itself, the expanding and contracting distance increases and thus a crack occurs, whereby SJR is adversely affected and thus reliability of the entire package is deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.